This proposal aims at a delineation of the immunologic features of colorectal carcinomas in rats and the creation of an immunotherapeutic model, in which the immunologic mechanisms are possible to analyze in detail, including the relationship to chemotherapy. The blocking phenomenon and various ways to manipulate cell-mediated and humoral antitumor immune responses will be given special attention. The relationship between embryonal antigens of rat colon mucosa and colon carcinoma antigens will be analyzed and the possible function of embryonal antigens as tumor rejection antigens will be studied. It will also be studied in human patients whether gastro-intestinal carcinomas and various premalignant lesions have crossreacting antigens.